1. Field of the Invention
This invention relates to a method for the optical resolution of DL-.alpha.-phenylglycine. More particularly, this invention relates to a method for obtaining D-.alpha.-phelglycine by the optical resolution of DL-.alpha.-phenylglycine.
2. Description of the Prior Art
D-.alpha.-phenylglycine is known to be a useful starting material for preparing synthetic penicillins, in particular, ampicillin which has a broad antimicrobial spectrum, and a demand for a method for producing D-.alpha.-phenylglycine in large amounts and at low cost has increased in the field of synthetic penicillins as disclosed in J. Chem. Soc., 1962, pp 1440-1453 and U.S. Pat. No. 2,985,648.
The compound .alpha.-phenylglycine, one of the .alpha.-amino acids, is not a naturally occuring compound and is obtainable only by chemical synthesis. In conventional processes for the production of .alpha.-phenylglycine the product is usually a mixture of DL-forms comprising an equal proportion of the D-form and the L-form. It is well known that synthetic penicillin having an antimicrobial activity can be obtained only from the D-form and, therefore, the above DL-mixture should be optically separated to obtain only the D-form of .alpha.-phenylglycine.
Various procedures for the optical resolution of DL-.alpha.-phenylglycine have heretofore been proposed. Typical procedures include a method comprise reacting DL-.alpha.-phenylglycine with d-camphor sulfonic acid and fractionally crystallizing the two resulting diastereoisomers by taking advantage of the difference in their solubilities, a method comprising converting DL-.alpha.-phenylglycine into an N-formyl derivative thereof, reacting the thus obtained N-formyl derivative with brucine and separating the resulting diastereoisomers by taking advantage of the difference in their solubilities and a method comprising converting the DL-.alpha.-phenylglycine into an N-acyl derivative thereof, reacting the thus obtained N-formyl derivative with brucine and separating the resulting diastereoisomers by taking advantage of the difference in their solubilities and a method comprising converting the DL-.alpha.-phenylglycine into an N-acyl derivative thereof and separating the N-acyl derivative into the optically active components by the activity of microorganisms.
However, the above conventional procedures are disadvantageous in that they require complicated resolution operations and, when the resolution is conducted via diastereoisomers, they require specific reagents which must be optically active, and further recovery of the reagents using an acid or an alkali is necessary.